1. Field of the Invention
The embodiments of the invention generally relate to electroplated metal integrated circuit features and, more particularly, to a structure and method for an improved high aspect ratio electroplated metal structure, such as a copper or copper alloy interconnect, for a semiconductor device.
2. Description of the Related Art
A semiconductor device, such as a field effect transistor (FET), is often formed with both back end of the line (BEOL) contacts to the gate and source/drain regions of the device to turn the device on/off and to allow current to flow through the device, respectively, and a middle of the line (MOL) contact to the body of the device between the source/drain regions to adjust threshold voltage (Vt). Traditionally, conductive metals, such as Tungsten (W) and Aluminum (Al) have been deposited (e.g., by chemical vapor deposition (CVD), sputtering, etc.) into patterned vias in order to form both MOL and BEOL contacts. Recently, because of its lower electrical resistivity copper and copper alloys, which require plating, have become the preferred metal for filling BEOL contacts and have also become the subject of new development and research for filling MOL contacts.
Unfortunately, as circuit densities are increased, the aspect ratios for both MOL and BEOL contacts has increased and adequately plating such high aspect ratio contacts has proven difficult. Specifically, as circuit densities increase and device sizes are scaled, the width of both MOL and BEOL contacts is decreased; however, the thickness of the dielectric layers in which these contacts are formed has remained the same. Consequently, increased circuit densities have resulted in high aspect ratio contacts (i.e., contacts with high height to width ratios). For example, circuit designers currently require MOL and BEOL contacts with aspect ratios that are greater than 6:1 and oftentimes greater than 10:1. When conventional plating techniques are used to fill these high aspect ratio vias, seams and voids develop within the contact structure and these seams and voids inevitably affect contact performance. Therefore, there is a need in the art for an improved high aspect ratio electroplated metal structure, such as a copper or copper alloy contact, and method of forming such an electroplated metal structure.